1. Field of the Invention
The present invention relates to an apparatus for semi-continuous, vertical casting (casting under closed molten alloy head, or "hot top" casting) in water of the light alloys in general, and of aluminum and its alloys in particular. The apparatus is equipped with coupling means between the ingot mold and the casting equipment, which are structured so as to eliminate any risks of explosion during the casting due to the liquid metal possibly coming into contact with the cooling water.
2. The Prior Art
It is well known that the apparatuses for carrying out the casting of metal alloys, and in particular of aluminum and its alloys, in water, are based on the principle that the liquid metal is cast by gravity. The casting takes place intermittently inside an ingot mold or die of tubular shape, arranged with its main axis being vertical. The mold is surrounded by pressurized cooling water which circulates inside a water tank having a substantially annular shape and arranged externally to and coaxially with the die. The external wall of the die forms the inner wall of the water tank.
The tight seal between the die and the upper and lower walls of the water tank is secured by gaskets. In the so-called floating-die casting apparatuses, the coupling of the die inside the water tank is achieved by inserting the die downwardly from the top into the water tank. A flange of the die is fastened to the upper surface of the water tank.
In the most recent types of apparatuses (known as "hot top" apparatuses), the matrix is inserted inside the water tank from the bottom upwards, and then is anchored to the base wall of the water tank by means of a fastening flange or edge protruding from the bottom end of the die.
The "hot top" type apparatuses furthermore use a connection cap between the liquid metal feed opening provided at the bottom of the molten metal basin and the top portion of the die. The connection cap performs the function of containing and guiding the liquid metal until it reaches that region of the die in which its solidification begins.
The casting in water of the light alloys according to the "hot top" technique and apparatuses can be dangerous. If a sealing gasket fails or the die is not perfectly anchored to the water tank, water can penetrate the interior of the mold, thus coming into contact with the metal in the molten state, causing explosive reactions. These explosive reactions are triggered more easily if substances, such as iron oxides or the like, are present, which can act as catalysts in the oxidation of aluminum, with hydrogen being formed. The risks of explosions can be practically excluded with the "floating-die" casting apparatuses, where the die is inserted from the top down into the water tank. The upper flange or peripheral edge of the die can prevent liquid metal from flowing towards the water tank, and water from flowing towards the die. However, such a drawback can still occur with the casting apparatuses of "hot top" types.
In these kinds of apparatuses, the interface region, i.e., the region in which the guide cap, which guides the flow of the liquid metal entering the die, rests against the die (or ingot mold) and/or its lubricating ring. These are critical elements and imperfections in the mutual coupling of these elements can cause metal leakages to occur which, by solidifying between the interfaces, lead to the formation of sub-skin surface faults in the shaped product, and therefore to product scraps. Therefore, in practice, in order to prevent such dangerous drawbacks from occurring, the dies and the relevant cap should be submitted to a continuous and careful monitoring and restoration. If these measures are insufficient, the dies will have to be removed and replaced by other dies, and repaired out of line. In these apparatuses, the dies must be inserted inside the water tank from the bottom upwards, in order to enable them to be replaced without the liquid metal feed system having to be dismantled.
As already stated, this method of coupling the die and the water tank with each other causes the risk that if the annular tight-sealing gaskets, in particular the top gaskets, fail, the water pressure existing inside the water tank would enable cooling water to leak through the cap-die interface and enter the interior of the die. This would cause a violent explosion to occur, with jets of liquid metal being projected through the casting channel.